While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, deep-ultraviolet lithography is thought to hold particular promise as the next generation in microfabrication technology. In particular, photolithography using a KrF or ArF excimer laser as the light source is strongly desired to reach the practical level as the micropatterning technique capable of achieving a feature size of 0.3 μm or less.
As the base resin in a resist material having transmittance to light of an excimer laser, especially ArF excimer laser having a wavelength of 193 nm, polyacrylic or polymethacrylic acid derivatives and polymers comprising aliphatic cyclic compounds such as norbornene-maleic anhydride copolymers in the backbone are used. For the base resin used in chemical amplification type resist compositions, not only an acid liability closely related to resolution, but also etching resistance and substrate adhesion are required. In the above-described resins, it is intended to accomplish such distinct characteristics by using a plurality of monomers having different properties to form a complex copolymer. However, these resins are not yet satisfactory on the practical level.
More particularly, monomers having as suspending groups polycyclic hydrocarbon groups such as adamantyl, tricyclodecyl and norbornyl are used for imparting etching resistance, and monomers having as suspending groups polar groups such as hydroxyl and carboxyl groups are used for imparting substrate adhesion. However, in a system where an extremely hydrophobic monomer for imparting etching resistance and an extremely hydrophilic monomer for imparting substrate adhesion are admixed, it is difficult to effect uniform polymerization reaction. Due to side reaction, homopolymers and undesired block copolymers can form. If the polymer product thus obtained is blended in a resist composition, this resist suffers from drawbacks including uneven dissolution due to in-film delamination, pattern collapse due to peeling of highly hydrophobic sites, and swelling due to random penetration of a liquid developer to highly hydrophilic sites. Even though the etching resistance is improved, the resolution of the resist is extremely reduced.